All crystalline materials have some level of defects. There are a number of different types of crystal defects, and they are generally categorized as either point defects, linear defects, or planar defects. Point defects are typically places where an atom is missing or irregularly placed in a crystalline structure. Linear defects are typically groups of atoms in irregular positions in the structure. Planar defects are typically interfaces between homogeneous regions of the material.
Crystalline materials are used in a number of different manufacturing processes. Depending on the process and intended application, they are typically used because of some beneficial property of the material. As an example, crystalline silicon materials are used in producing semiconductor devices because conductivity of the material can be controlled based on a concentration of impurity atoms in the material. A number of other crystalline materials are used in semiconductor or other device or material processing operations.
Because crystalline materials are typically used to exploit some particular property of the material, it is generally important to control characteristics of the material to ensure the particular property is provided within some threshold limits. Some characteristics that may be controlled include impurity levels and defect concentrations. These characteristics may affect the particular property directly or may have some other undesirable consequence. For example, crystalline defects in semiconductor devices may not have a significant effect on bulk conductivity, but they may be the source of leakage current that renders the device inoperable. Generally, there is a correlation between crystalline defect concentration and yield or performance of semiconductor devices, especially in microprocessor devices, dynamic random-access memory (DRAM) devices, static random-access memory (SRAM) devices, complementary metal-oxide semiconductor (CMOS) imaging devices, and other devices.
The primary methods for identifying crystal defects are destructive cross-sectional or plan view imaging techniques (e.g., using transmission electron microscopy, secondary electron microscopy, and the like). Oftentimes defects in semiconductor processing are not identified until a device fails end-of-line (EOL) at electrical or yield testing. Thus there may be a delay of weeks or even months between a crystal formation process and analysis identifying a crystal defect as a culprit for device failure or performance degradation.
Besides being destructive, conventional imaging techniques are too slow to allow in-line defect monitoring. Also, the amount of data that can be practically produced is too small to satisfy the need. The probability of a cross-section intersecting a point or linear crystal defect is low. Further, depending on the plane, crystal defects may not be visible even if captured in a cross-section or plan view image. It is estimated that sensitivity of cross-sectional and plan view imaging techniques to crystal defects is several orders of magnitude lower than what is needed for proper process control. Thus, there is a need for improved methods for detecting defects in crystalline materials.